1. Field of the Invention
Embodiments of the invention relate to a method and apparatus for controlling a write parameter. More particularly, embodiments of the invention relate to a method and an apparatus capable of controlling a write parameter in accordance with a voltage variation supplied to a pre-amplifier.
This application claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2006-0010857, filed on Feb. 3, 2006, the disclosure of which is hereby incorporated by reference herein in its entirety.
2. Description of the Related Art
Generally, the amplitude of write current supplied to a disc within a Hard Disc Drive (HDD) is defined in relation to the power supplied to an associated pre-amplifier. That is, the rise time (dt) of the write current changes in accordance with a voltage (dv) supplied to the pre-amplifier, as follows:
      dt    =          N      ⁢              di        dv              ,where “di” is current and N is a constant related to the number of turns.
As the operating speed of devices, such as HDDs, increases, shorter and shorter write current rise times are required. To reduce the rise time, the supply voltage applied to the pre-amplifier is increased. However, there are well-understood, practical limits on the supply voltage regardless of the operating speed of the overall device. For example, assuming an HDD uses supply voltages of +5V and −5V, the −5V supply voltage may be supplied by a voltage a regulator circuit receiving a supply voltage of 12V. The +5V supply voltage on the other hand may be supplied using a switching mode power supply (SMPS).
Under these assumptions, the −5V supply voltage may be readily and constantly maintained an output from the regulator. However, +5V supply voltage supplied by the SMPS will vary. As this supply voltage varies, so too does the rise time of a write current supplied from the pre-amplifier to a write head of the HDD.
Figure (FIG.) 1 is a graph showing the relation between write current and a Bit Error Rate (BER) as a function of two exemplary voltage variations. Referring to FIG. 1, when the voltage provided by the SMPS is reduced, the rise time for the write current increases, thereby resulting in greater bit errors in the written data. Such a result impairs the reliability of the HDD.
For example, when voltage V2 of FIG. 1, as supplied to the pre-amplifier of an HDD, falls from +5.0V to +4.5V, the bit error rate for the HDD increases significantly over an analogous BER for voltage V1 which is maintained at +5.0V. Therefore, when the voltage supplied to the pre-amplifier decreases from +5.0V to +4.5V, the write current must be increased from 30 mA to 50 mA to compensate.